It would be better to use GCP’s, but the problem you are going to run into with any GNSS collection that is not localized is that you are going to report either ellipsoid, geoid or orthometric height values. None of which are relevant to true ground.
Localization is a process that ties GNSS (lat/lon) values to a cartesian (flat plane X/Y/Z) coordinate system, but uses the elevation value derived from an on-the-ground vertical benchmark.
How are you verifying that you are getting 1-2 meter accuracy? The best thing you could do with a phone is to use an app that does observation averaging. If you let it sit there for at least 5 minutes then you will get meter accuracy. It’s very doubtful you will get anything better than that without PPK or RTK corrections.
If you are only really concerned with map to map relative accuracy (lining up) then check out this thread. Otherwise you are going to need another solution to get better GCP’s.