Yes — as a practical guide, this can work fairly well. Exposure is based on the relationship between ISO, aperture, and shutter speed, so if you match those settings, the phone’s suggested shutter speed should usually be close enough to use.

A few caveats:

• It won’t be exact. Film and digital sensors don’t respond to light in exactly the same way, so ISO matches are only approximate.
• Real cameras and lenses may not be perfectly calibrated, so marked shutter speeds, apertures, or ISO can be slightly off.
• For very long exposures, film reciprocity failure can make the film need different exposure than a digital device suggests.

So for normal shooting, your phone can serve as a rough meter, but expect small differences and bracket if the shot matters.

The bigger issue is convenience: using a phone for every shot gets tedious, and it’s easy to forget to re-meter when the light changes. Replacing the OM-1 meter battery will be much easier and more reliable in regular use.