Look for this option in the conversation menu. If it is not there, you can use third-party applications such as Call Recorder.
Some phones restrict this option due to legal issues.
I am using the OpenCalls.me application. It's convenient and free. In addition to recording conversations, I also keep track of all calls. Then I listen to conversations directly from the device.
If you have a Samsung smartphone, there must be built-in functionality. During a call, click on the three dots (menu) and click on the "Record" button. If it's another company, then you will have to download various applications (for more information about this - https://mirsmartphonov.ru/kak-zapisat-telefonnyj-razgovor-na-smartfone/)
For iPhone there are 2 options - download the TapeACall app or buy the specially Call Recorder . (More information can be found on the website above)