I’m in Mexico my phone is for USA and I make a purchase

Thank you for reaching out. 🤗

There are many parameters that need to be taken before changing regions because currency valuation is not the same across various regions.

If you are changing regions:

• Spend any balance remaining on your Apple Account. If you’re not sure whether or not you have a balance, check your Apple Account balance.
• Cancel any subscriptions that block a country or region change and wait until the end of the subscription period. 
• Wait for any memberships, pre-orders, movie rentals or Season Passes to complete and wait for any pending store credit refunds to process. You can cancel a pre-order.
• You may be required to enter a valid payment method for your new country or region. See what payment methods you can use.
• Redownload your apps, music, movies, TV shows and books on any devices that you might use to play or read them in the future. Some types of content might not be available in your new country or region. Learn what types of content and services are available in your new country or region.
• After you update your Apple Account billing address and payment method, you can upgrade your iCloud+ plan using the pricing in your new country or region.
• If you need to empty your balance, Contact Apple Support to request a reset of your account balance to zero.

For full details, learn how to → Change Regions for step-by-step instructions.

Good luck! 👋🏼😉

Smiliñ 😎 Brian

Follow the instructions provided on the link below...

Change your Apple Account country or region - Apple Support

Before you can change your region your Apple Account balance must be zeroed out and all subscriptions canceled.