Just after recommendation for a magnetic air vent mobile phone holder.
iPhone (not plus) with Spigen case, so I want one where I can attach magnetic disk to the inside of the case and have grip through the case.
Many on eBay but I have no way of verifying magnet strength.
Get the Spigen magnetic vent mount. I've got one and it held my Galaxy Note 4 with a Spigen Slim Armour case no problems at all.