in a web environment, php outputs whatever html you tell it to. so the more html you know, the better your design might be. that being said, if youve been happy with your designs so far, than you'll be happy with whatever you tell php to output.
hard to explain....but as you come to understand what php is, you'll get it.
instead of recomending a hard copy book, i can recomend a free online book. practical php. if you work your way through that, you should get a decent understanding.