I have iPhone 6and iOS 12.5.4.version. But gpay and phonepe not working properly?

Those apps require a higher version of iOS than your phone is capable of running.

If you want to use them, you will need a new phone.

Is Gpay, Google Pay? If it is, your phone should be able to support Google Pay as what is required is at least iOS 11. If Gpay is something else, please clarify. I don't have a clue what phonepe is however.