my i phone will not let me select the option of none when im trying to delete my debit card

Note that you can't select None as your payment type if...

• If you have a subscription that automatically renews View, change, or cancel your subscriptions - Apple Support
• you're a family organizer Family Sharing - Apple Support
• you have an unpaid balance or payment due See your purchase history in the iTunes Store on a Mac or PC - Apple Support

See this for more information:

If you can't choose None when you edit your Apple ID payment information - Apple Support