hahahaha,

funny topic, but let me explain!!

If she enjoys talkin to her husband in the phone while having sex with you, it is obvious that she probably miss having sex with her husband,

So her sexual desire is being fulfilled by you, and she still misses him (possibility), so to aggregate these desires she probably does this,

But i would suggest you, explain her that it is not very good, and also tell her to control herself, help her to get in touch with her husband,

It sounds quite real to me,

it is all called female psychology,

Well, do what is best for you and her!