That phone number is a back up contact. Primary is still Telegram for now... learning the ins and outs of Matrix and XMPP.
The bonus to moving accounts to use a sip number - the same lack of attachment to a sim card means I can hop mobile cariers all I want without the hassle of updating banks and utilties and whatever else.
Same voip carrier lets me add a number for like $3 if I later feel I need more seperation.