I use 2 types of mechanical coupling between different pieces, tripod thread + velcro. Phones have velcro on their backs and so have power banks and pouches protecting from rain. The disk has opposing velcros on 2 sides and it is connected with ballhead tripod mount to the accessory bar. You can attach power bank underneath the disk or sandwich it between disk and phone. All can be moved to a car and mounted there, put on a QR mount on another bike etc. The key is to standardize couplings just like with USB for electric.