How do I connect Zoom H1 Recorder to an Android smartphone? In particular, I want to connect the recorder to a Samsung S6 device I can borrow. The idea is to shoot videos from the phone by taking the audio from the Zoom H1.

I have done this for DSLRs. Is there a way for phones?

Regards.
You need to mod a 4pin Jack cable to make your phone detect a headset+ microphone combo when external Mic is plugged.
The ground is the first ring (nearest to cable), microphone is second ring.
Last two are stereo audio.