Timpson’s will replace a phone screen for £40 inside an hour.
While I appreciate this is quite a sum it’s far less than the cost in time and effort of pursuing this beyond shop level.
TBH I wouldn’t risk putting a heavy object, relative to the lightweight material, in the pocket. The phone will be bouncing up and down for some distance putting strain on stitching and material in pocket probably designed for little more than a house key or emergency cash. Faulty stitching shouldn’t happen but it doesn’t seem a very secure place to carry an expensive phone.
