How to use PayPal for purchase on my apple phone

You can set Pay Pal as a payment method for your Apple ID to be used in the iTunes and App Stores by following the steps here if its supported in your country: link-> Change, add, or remove Apple ID payment methods - Apple Support

See here also: link-> Payment methods that you can use with your Apple ID - Apple Support

You cannot use Amazon gift cards on Apple's iTunes or App Store, but you should be able to redeem the Amazon Gift Card onto the Amazon App to buy things form Amazon.com.