Thanks for contacting TextNow Support!
If you order a replacement phone, we won't charge you for another plan, and the service will transfer over to your new phone automatically when you receive it and log into TextNow.
In your particular case, you can log into your account here and tap on the phone you'd like to order, and we'll charge you for the phone only. You bill date will remain unchanged.
If you need any assistance, please give us a call at TextNow Support at the numbers you see below and we can help!