In IMS VoLTE call, how to identify IPs assigned to phone numbers from control traffic (SIP, SDP …)?

Question

In IMS VoLTE setting of a telecom network, what part/field of which type of packet (SIP, SDP, others...) gives authentic information of MSISDN-IP mapping? From a sample traffic, I need to find out information from control traffic about what IP is assigned to what phone number. In the sample traffic, I see a lot of protocols (SIP, SDP, RTP, DIAMETER, ISUP, ....). I require to find out IPs assigned to phone numbers. I know RTP flows between end devices (phones), but I need to find out IPs before the call is established...