A magnetic phone holder should be rated for the complete load, not the phone alone. Measure the phone, case, camera cover, and any metal ring. A 210-gram phone with a 45-gram case already weighs 255 grams. Add a 20-gram accessory, and the holder carries 275 grams.
Choose a rated load at least 1.5 times higher. For 275 grams, a 415-gram rating gives useful protection against braking, bumps, and vertical vibration. This is not excessive. Road shock changes the force. A holder that feels strong on a desk may slowly slip in a moving vehicle. Check the rating in the holder’s technical sheet, not only its marketing description.
The Wireless Power Consortium’s Qi2 documentation supports magnetic charging up to 15 watts, but charging power is not mechanical holding strength. These are separate specifications. IEC 62368-1 also addresses equipment safety, not a universal magnetic retention rating. I initially treated a strong magnet as enough. That was careless. Test the assembled setup for ten minutes, then repeat it with the phone tilted and the vehicle moving. If the case flexes, the magnetic connection weakens. Remove thick cards and uneven camera protectors before testing. Some load figures may be optimistic, so leave more margin than the printed minimum.