As I could not find it on the web I created it myself. Here is the standard iPhone ring tone, but incremented. It gets louder during time. The standard progressive iPhone ring tone has already been downloaded 3002 times.
Download the ring tone here: iPhone standard incremental ring tone
Download the ring tone file. Unzip it. Double click it. iTunes will automatically add it to your ring tones folder in your iTunes Music Library.
Synchronize your iPhone with iTunes.
Choose the ring tone in the setting menu of your iPhone.