You need to decide when to allow the use of mobile phones in polling stations and make this clear to polling station staff in your staff training.
Our advice is that you should not allow photos to be taken inside polling stations. The law relating to obtaining information in polling stations and disclosing such information is complex and there is a risk that someone taking a photo inside a polling station may be in breach of the law,1
whether intentionally or not.
You could decide to display a notice inside polling stations to make clear that photography of any kind (including photos taken on mobile phones) is not permitted.
While you should ensure that all polling station staff are aware of this guidance, they should also understand that some voters with sight loss may need to use apps on their mobile phone or other devices to help them to read documents, and they should allow them to do so.