Hi @JérômeD :
Do you want to upload the photo taken over the phone to the SharePoint library?
If so,I've made a test for your reference:
1\Add a camera control(Camera1)
2\Create a flow('PowerAppV2->Compose,Createfile')

/*This flow's trigger is PowerAppV2*/
3\Add a button and set it's OnSelect property to:
Set(Thepic,JSON(Camera1.Photo,JSONFormat.IncludeBinaryData));
Set(Base64Only,Mid(Thepic,Find(",",Thepic)+1,Len(Thepic)-Find(",",Thepic)-1));
'PowerAppV2->Compose,Createfile'.Run("ThePic.jpg",Base64Only)
TheResult

In addition,your flow did not add the file suffix ".jpg" when setting the name of the file to be created
Best Regards,
Bof