An external mic such as the Røde VideoMic Me Directional Mic for smartphones can be added to your phone via the 3.5mm jack socket. In this case the VideoMic is a mini shotgun mic, only c10cm long. As this plugs directly into the phone (no lead) the phone and mic need to be outside (or nearly so). There is Røde app to control recording quality and even schedule recordings.
Things to bear in mind:
- Some microphones get their power via the cable. Phones may not be able to supply the required current.
- The 3.5mm jack socket on some phones is only for headsets and without an adapter cannot be used to plug in a microphone.