It should not be needed to sync often, ideally just the 2 times of the year when we change daylight savings.
If it is needed more often it are often to blame on the RTC battery or the battery itself if it is one of those cameras.
I have GPS on my cameras so that way the time get synced every time the camera get GPS lock, and so i just have to change to compensate for daylight savings 2 times a year.
A proper functioning camera still should keep the time/date saved / in order for a week of no activity.
But sync to phone time you have to use the camera APP, as that are sort of the platform the 2 use to talk together, as far as i know it is not possible to do automatic if you had the wifi on both devises.
Though computers can sync to a master server online, i dont think that is the case with phones and dashcams.