You will more then likely still be seen as a mid level developer for several years by company HR groups until you add more of the enterprise senior level skill sets to your resume experience. This will normally involve you conducting the development of software in high traffic sites, dealing with load balancing million+ visitor websites across several servers being served behind a top tier CDN, handling large scale caching on the code and database level, managing multiple terabytes or petabytes of storage, working with integrating Akamai into sites along with their security features and API, etc.

You will normally also be an expert at certain database technology included PostgreSQL, MySQL/MariaDB, MongoDB, and caching technology Memcached, Redis, Zend Optimizer, OpCache, etc.

You will also need to be able to engineer solutions that scale appropriately including hardware and software, train other developers and sometimes system administrators, work with senior management, write tons of detailed documentation, conduct security reviews, developer interviews, and more. Also conducting performance optimizations at the high and low level is also standard as you might have to write custom php extensions in C for functionality you might need or want more of a speed boost out that is not offered by default.

Once you get to this level most of your job will involve many questions from other developers or senior managers about higher level engineering and architectural work as you almost find yourself in a managerial type role. This will normally involve more reading and writing development guidelines, helping with writing policy, security documentation and guidelines.

Just remember, learning the programming language and a framework is only a small part of becoming a senior developer. Only until you have the skill set to do the upper tier work that is in high demand and low supply will you then be in the senior developer / engineer group. It is not hard to make it there, but it does take some time and experience. As getting the jobs that involve more development and hard high end integration work are very competitive and normally have some very high requirements for entry.

I recommend checking out the senior developer and engineering jobs at large companies to get a better idea of what many companies are looking for and start working towards those goals, especially if the companies are close to you.

Thanks a lot for your detailed answer. I was looking exactly for this kinda of advice :) I'll remember your golden words.

Management bits doesn't really interest me but knowing what are so called enterprise skills are and where should i head to was really important to me. Well answered.

Go/Node/Scala/Elixir all are good choices - Go for scalable distributed multi node deployment architectures.

There is nothing called senior skills. As long as you cover a-z in given project from css, caching to backups an monitoring. you're pro.