Backend PHP PBX Developer [On-site Luxembourg]

About Mixvoip

Mixvoip is a Luxembourg-based company providing cloud telephony, smart networking, and high-speed internet services.

We build and operate communication systems that businesses rely on every day. We are looking for a developer who wants to work close to telephony infrastructure and help improve the platform behind our cloud PBX services.

Your level of experience is not the deciding factor. We are open to junior developers who want to grow into the role as well as experienced developers who can take ownership quickly and help shape the platform.

About the role

You will join our PBX development team and work on the systems that control call routing, device provisioning, configuration generation, and telephony automation.

This is not a traditional web development role. There is no frontend, UI, or CSS work. Most of your work will involve backend services, CLI tools, scheduled jobs, APIs, configuration files, and direct interaction with our VoIP infrastructure.

You will use PHP and Linux to develop and maintain features for our PBX platform.

Depending on your experience, you may start with smaller, well-defined tasks and grow into more complex responsibilities, or you may take ownership of larger areas from the beginning.

This role requires regular on-site presence at our office in Luxembourg and is not a remote position.

What you will do

• Develop and maintain features for our cloud PBX platform

• Implement call-routing rules and telephony configuration

• Generate PBX and device configuration files

• Automate the provisioning of Yealink, Gigaset, and Grandstream devices

• Integrate internal systems and external telecom APIs

• Build CLI tools, background workers, and scheduled jobs

• Maintain configuration templates using Twig

• Investigate call-flow, provisioning, and integration issues

• Work with logs to troubleshoot telephony problems

• Document PBX behaviour, code, and operational workflows

• Improve the reliability and maintainability of the platform

What we are looking for

We are interested in both potential and experience. You do not need to match every point.

• Knowledge of PHP or another backend programming language

• Comfort working in a Linux environment

• Understanding of APIs, databases, JSON, and structured data

• Interest in VoIP, telephony, networking, or infrastructure

• A methodical approach to debugging and problem-solving

• Clear communication and a collaborative attitude

• Willingness to learn unfamiliar systems

• Ability to work regularly from our Luxembourg office

For junior candidates, internships, apprenticeships, school projects, open-source work, home labs, and personal projects all count.

For experienced candidates, we value ownership, system design, production troubleshooting, performance awareness, and the ability to improve existing systems.

Useful experience

Previous experience with any of the following is helpful, but not required:

• SIP

• Asterisk

• PBX systems

• Call routing and dial plans

• VoIP device provisioning

• Twig configuration templates

• Docker

• Cron jobs and background workers

• IP networking, routing, DNS, NAT, and firewalls

• Telecom vendor APIs

• Monitoring and troubleshooting production systems

Junior candidates are not expected to know all of this already. Senior candidates are not expected to have worked with our exact technology stack.

How the role adapts to your level

If you are earlier in your career

You will receive guidance, learn how the platform works, and begin with manageable tasks such as:

• Updating configuration templates

• Fixing provisioning issues

• Improving existing PHP scripts

• Investigating logs

• Making small API changes

• Testing routing rules

• Writing documentation

As your knowledge grows, you will gradually take ownership of larger PBX features and automation projects.

If you are more experienced

You may take ownership of larger technical areas, including:

• Designing new PBX capabilities

• Improving platform architecture

• Leading complex integrations

• Strengthening reliability and observability

• Reviewing code and technical approaches

• Mentoring less experienced developers

• Helping define engineering standards and long-term improvements

What will make you stand out

• Experience with SIP, Asterisk, FreePBX, Kamailio, 3CX, or similar systems

• Strong PHP and Linux experience

• Experience running production backend or infrastructure systems

• Personal projects involving networking, telephony, automation, or self-hosting

• Experience with Docker, servers, routers, or home labs

• Strong troubleshooting and documentation habits

• Practical use of AI coding tools in your daily workflow

• Genuine curiosity about how phone calls are routed and connected

A new way to apply: join Mixvoip’s success story

Join Mixvoip and you won’t just be connecting businesses to high-speed internet, fiber, satellite, phone, or mobile networks, you’ll be connecting people, forging relationships, and making a real difference in our story.

So, if you’re prepared to embark on an engaging journey and play a pivotal role in Mixvoip’s saga, here’s an unconventional route to apply

We invite you to record a brief presentation video with your smartphone. Share why you’re drawn to this role or pose any questions or doubts you might have. It’s about keeping the conversation open and engaging! Please remember to attach your CV in PDF format too.

Instead of a conventional cover letter, we’d like you to employ an AI of your choice. This not only mirrors our technology-focused approach, but it also allows you to showcase your adaptability to new tools. It’s less about the letter, more about your interaction with AI that we’re keen on.

How to apply

Send us:

• Your CV in PDF format

• A few sentences explaining why PBX and VoIP development interest you

A short introduction video is welcome, but optional. You may also use an AI tool to help prepare your application, although this is not required.

We care more about your ability, curiosity, and motivation than about your job title or number of years of experience.

Whether you are starting your career or bringing years of experience, we want to hear from you.

PS: Want to know who you’ll be journeying with? Meet me, Christophe Laures

I’m 33 years old and have been part of Mixvoip for the past 10 years. Today, I lead the development of our PBX platform, working with the team to create the best possible experience for our customers.

My main focus is driving the evolution of our newest PBX system so that our customers always have a reliable and versatile communication tool they can depend on.

I enjoy solving complex challenges and finding clean, practical solutions that make a real difference. I’ve always been passionate about computers and technology, which is what originally led me into this field.

Outside of work, I enjoy spending time outdoors. You’ll often find me hiking with my wife and our dog, recharging and getting ready for the next technical challenge. And on rainy days, I’m usually at home playing computer games.