> over time lisp would change to become more like PhP.
A lot of things are so wrong in this statement.
First of all, PHP isn't bad. Don't get me wrong I don't like it (I also don't like Go but that's another story) but it has become so much better. Several of my colleagues use it (that's not the only language they use though) and believe me they are quite passionate about programming. Actually there is some zen in being able to use any tool life throws at you to solve some practical problems.
Second, you are comparing family of languages to the one particular language. This doesn't do justice to both.
Third, if the comparison with PHP was another way to say that Lisp would become worse then here is another thought. It won't. Every mainstream language I know is becoming better in a sense of better defaults and FP features. Java has got lambdas. JS ES6 is going to have TCO and strict mode which fixes a lot of old vague behaviour. Yes, there are a lot of crazy stuff in those languages because their features weren't well thought out back in the day and now it's impossible to fix everything without breaking the core semantics and behaviour. Basically you can fix some things but you can't evolve one language into another.
Getting back to Lisp now. It doesn't need fixing. It has very basic and clear core which doesn't need to be fixed and a lot of advanced language features can be built upon it (and actually was built and are being built). Taking in account both that languages are becoming better with time and that Lisp has awesome core I don't see at all how's popularity can make it worse.
I'd suggest reading some PLT books or taking some related courses. It helps to get the whole picture. You won't love Lisp less (probably the opposite) but you'll accept other languages more. :)
I have to add I'd prefer something Lispish over anything else any day of the week. I'm looking into Clojure(ClojureScript). It's not as elegant as original Lisps and Schemes but it's tradeoffs come from real world use cases (running on top of JVM and JS). Even with them it's an awesome language.