Have SiriusXm on my I phone. Can my wife use it also on her Iphone?

Assuming you each have your own unique Apple ID, you can use Family Sharing to share content between the two of you. What you need to find out from SiriusXM however, is each phone can listen to Sirius at the same time, which may require you to pay for a family plan.

Your question requires two steps. One to have a Family Share account with Apple and this link explains that --> Family Sharing - Apple

And you need to contact Sirius about your account and what it permits or doesn't permit.