Resolution size to for cell phones

Hello Everyone,

I am using Toon Boom Essentials, and I am working on an animation project for a client, and the entire project was done with a stage size that is 1920w and 1080h. The client would like to view the completed project by way of a cellphone. My question is how can I make this large file compatible, or accessible on a cell phone, without too much loss of resolution?

Any assistance on this matter will be greatly appreciated

Thank You