checking ur partner's phone is not a big deal based on ur terms of agreement in ur relationship and the understanding both of u av about each other and most importantly d TRUST. But y should ur partner get angry over u checking his or her phone if he or she does not av a skeleton in his or her cupboard.
if u have d heart to pierce any part of ur body as a grown up apart from the necessary part, d ears then u av the got to do some other dangerous thing. frankly speaking if u r christian it not biblical