The simplest, lowest-tech option—beyond operating a recorder while you blather over the speakerphone—is a cable: the Olympus TP-8 Telephone Pick-up Microphone for under $20. It doesn't digitally capture from your iPhone. Instead, it has a microphone built into the earpiece. Plug the 3.5mm plug on the other end into a recorder. Hold the iPhone up to your ear to talk normally. The TP-8 captures each side of the conversation from what comes out of the iPhone's ear speaker, while you can still hear the conversation.
3. Force close and reopen the Phone app. To force close Phone, on iPhone X and later swipe up until you see the apps in task view, then swipe up again on Phone.

A busy greeting should tell callers that your phone lines are currently in use. You can direct people to wait on hold or leave a message. For example, “Hello, you’ve reached [company name]. Our representatives are currently helping other customers. Please stay on the line to speak with the next available team member, or press one to leave a message and we’ll call you back.”
The length of the message counts too, so BT Mobile lets you store a maximum of 150 minutes at a time, with individual voicemails capped at seven minutes each. Some networks also limit individual voicemails to just two minutes.