No sure how this question relates to an AirPort Express, AirPort Extreme or Time Capsule. The printer and iPhone are both connected to the wireless network, correct?
If you cannot find the AirPrint printer from the iPhone, you might want to post in the iPhone support area to ask about this, as you will likely get a faster and more informed answer over there.
If you have a question about an AirPort Express, AirPort Extreme or Time Capsule, we can likely help on that. Please re-post.