How can I remove certain fields in the prefix component?

I am trying to create a field with only a single name textfield. Just name, no first name or last name.

And phone number not requiring area code.

You can use the Short Text Entry field and add it to your form. To do that, please check the screen animation below:

Unfortunately, it is not possible to remove the area code of the phone number field. However, you can also use the Short Text Entry field and enable the Input Mask for numbers only. 

I hope that helps. Let us know if you have any questions.