How can I access past call logs on iPhone 12?

Your phone only stores a finite number of calls it received. If you need to find a number and it's not in your Recents in the Phone App, you can typically log into your carrier account online and see a more comprehensive list of the calls you've made or received.

Contact your carrier. The length of time cell phone companies keep call records varies by provider and type of information.  Some examples:

• FCC: Requires companies to keep call records for 18 months
• T-Mobile: Keeps call records for 7–10 years
• AT&T: Keeps call records for 7 years
• Verizon: Keeps records for 2 years