What exactly is called Patched Phone? A Non PTA Approved Phone (Rooted & changed IMEI from Nokia etc phone) Right?
What about Iphones? Since they can't be rooted thus no/minimal chance of IMEI change.
Patched phone is exactly what you said. IMEI is changed not necessarily to Nokia feature phones, but to any other PTA approved phone that is dead / non-functional. Lots of old scrap smartphones lying around with these repair shops that are already PTA approved, so you'll often see patched S10 and Note 10 with IMEIs from Galaxy S6/S7, Note4/5 and older phones like this.
There is (or at least was) a workaround for iPhones as well. It didn't involve changing IMEIs and was more expensive than the Android phone patching method, but what shopkeepers would do is register two phones for the price of one.
All newer iPhones have one IMEI for the physical SIM slot and one IMEI for the eSIM, so when registering a device on the DIRBS portal, the shopkeeper enters the IMEI of one iPhone's physical SIM slot, and the IMEI of a completely different iPhone's physical SIM slot, allowing him to register two iPhones for the cost of one.
This is why most iPhones you'll find will only have the physical SIM slot approved and the eSIM IMEI is not approved since most people don't use it and Jazz seems to be the only carrier offering it anyway.
However, PTA found about this and now when registering iPhones, there is a waiting period of a few days after you submit an application with the IMEIs. They have some way of verifying if both IMEIs actually belong to the same phone, and only once they do, a PSID number is issued allowing the phone to be approved.
So as far as I know, the method of registering two iPhones for the price of one is no longer possible, but I could be wrong.