Frankly, whether or not you use Ruby, PHP, C#, Java, Perl, or other language is fairly immaterial. What is more important is how well you know and can work with a given language. If you already are a fluent programmer in PHP and have or know where to get reusable classes, functions, templates, etc. so that you do not have to reinvent a lot of wheels, then PHP is likely going to be faster than using something where you need to learn a new language, discover what libraries exist for it that you might want to use, etc.
On the other hand, if your schedule allows it, there's certainly a lot to be said for learning another language. It broadens your skill base and usually ends up teaching you a trick or two that you find you can use with PHP or any other language.
But, unless you are a fairly experienced programmer in general and comfortable working with object-oriented techniques, I doubt that switching to Ruby will allow you to reach project completion faster than using what you already know.