No, I'm afraid not in the manner you remember or have used before. There are apps that enable you to put "quick dial" icons on the phone homescreen and, if you are jail broken, there are several tweaks in Cydia (the jail breaker's "AppStore") that allow you to quickly call a number.
But, there is nothing native on the phone or in iOS to allow you to create a one-number quick dial. Sorry.
Marilyn