We have tested several pieces of hardware for use with a roaming or studio style setup.
iPhone Mount for mounting an iPhone next to a Camera. This is the Joby GripTight Pro 2 Mount (Black/Charcoal) : https://amzn.to/43ug0Q6
You can use this Dual Flash Bracket 8in/20.3cm Camera Mount Tripod Bracket to connect to the DSLR camera and to connect the iPhone using the Joby amount above. Here is a link to these https://amzn.to/3Px4gXk
Here is another option for a mount. This one has more shoes for other connections and holds the iPhone on a slant which some people like. This one is called: ChromLives Camera L Bracket Mount Video Grip L-Bracket with Dual Flash Cold Shoe Mount and can be purchased here https://amzn.to/4amc3zh
Here are a few data cables that can also be used. Tether tool cables have been tested.
USB-a to USB-c connections https://amzn.to/3IMXyJd
USB-c to USB-b https://amzn.to/3x1t03w