What steps do I take to remove a phone number from a group text

If any of the members of the group are using SMS (green), you can't remove yourself. You will need to request that the other members of the group start a new thread without you.

Add and remove people in group text messages on your iPhone or iPad - Apple Support (CA)

Meanwhile, you can mute the conversation by going to the main conversation screen in Messages, placing your finger on the conversation, pulling to the left and tapping the purple bell icon.

CBMessages wrote:

What steps do I take to remove a person from a group text

Can only be done for a group imessage of 3 or more people, can't be done for group MMS.