I'm deciding between RoR or PHP still.
Just so you know, Ruby on Rails is a framework while PHP is a language. Perhaps you mean "RoR vs CakePHP" or "Ruby vs PHP"?
Whatever you do chose will come down to.... whatever you do choose. You don't have to choose LAMP for your web project. However, there are pluses and minuses for whatever you do chose.
Since you say you don't have any experience in anything but iOS development, I'd suggest looking in to other languages (Java, C# .NET, etc) and
NoSQL alternatives (Cassandra, MongoDB, etc) (actually, you should understand relational databases before going on to NoSQL, so learn MySQL) and possibly consider using those.
You're probably looking for an answer like "you should choose _ and _ because they work well together and are very reliable", but honestly I can't really give you an answer like that. I will say that learning the relational databases isn't hard at all, and I've heard that PHP is easy to learn, so that probably should be the route you go if you want to develop the server-side component of your app in the least amount of time.
However, having a good database design, MySQL queries, and good PHP code is a different story. :)