How do I connect to a printer via iPhone without Wi-Fi?

Hi,

Any information about the exact printer model?

For printing from an iPhone without a special app, an AirPrint-enabled printer is needed. As deggie mentioned, Wi-Fi is a requirement.

If necessary, it is possible to create a (temporary) local/private Wi-Fi network for printing purposes. For this, one could use almost any old Wi-Fi router (may be found in a thrift shop for a few dollars). The interesting section in this case is the LAN/WLAN. The Internet side (WAN) can be left unconnected.

You can't without WiFi.