PHP might be a good first language in your particular situation but I wouldn’t say that’s generally the case.
The first consideration is what you want to do with programming, and then you’d pick some somewhat sane language that does that (most languages are perfectly fine to start out with)
How you want to learn also affects what you’d start with, one might for example want to quickly be able to make things, get results, or one might want a fuller understanding and would therefore start with a language that deals more with plumbing (low level stuff that other things build on)
So if you’re exposed to PHP a lot and plan to continue to be so, then yes, start with PHP.
As for how to learn it, I suggest asking those that already know it if you know such people (maybe wordpress has an irc channel or something like that where if you ask very politely they could help you pick a resource, or if you’re not specifically looking to do something with wordpress, then PHP probably has an irc channel which would be an even better place to look for appropriate learning resources)