So far, you've received some good advice, but there is one critical piece of advice that's missing. And that's the fact that non-technical gatekeepers rarely have much leeway in giving you the benefit of the doubt.
So whatever you do, do not submit your resume in cold. Either try to contact the hiring manager directly, or try to get a non-HR employee to refer you.
Worst case scenario, that person you contacted will still tell you to submit your resume through the official web portal of the company and affix the right job number to it, but even if that's the case, you can still say that so-and-so told you to submit the resume through the web portal.
Personally, I used to work as an HR intern 25 years ago for a very large national laboratory, and when I received such resumes with referrals, I was instructed to make sure those resumes would show up on top of the screen in the database (and on top of the pile of resumes when on paper).
This was because our department didn't want to be accused of losing resumes. So if a cover letter mentioned an employee by name (as a possible referral), it was marked as such in the database.
I can't stress enough how critical this step is. If your resume doesn't match the right technical keywords, the non-technical HR recruiter (or the 3rd party recruiter) will just toss it in the basket, or place it at the very bottom of the pile (which essentially has the same effect). Because of legal requirements, we didn't actually throw away resumes into the basket (but you guys know what I mean).
So do whatever you have to do, do your research, go to meetups, go to job fairs, go to trade shows, don't be shy, use your LinkedIn network, use Twitter (many people have open DMs), try to reach the hiring manager by phone, guess someone's email address (but don't attach your resume unless they ask because most people are wary of viruses), etc. Just don't send your resume in cold.
On the other hand, PHP and C# are both object-oriented programming
languages, they are not the same, but they are similar, so they might
say: "You can work with us because of the resemblance between those
two programming languages / frameworks".
Also, when making this argument, do not stress the fact that Symfony/PHP are similar to C#/ASP.NET, that could easily lead to a religious discussion about programming languages (which is not what you want).
Instead, stress the fact that your ability to learn of programming languages is excellent.