Greetings!
I do food photograhy professionally
The OP's son is a restaurateur, not a commercial photographer, and I doubt if he is going to have the time, space, budget, and/or willingness to invest in a digitally converted view camera.
The first step in upgrading his camera is to find out the eventual usage of the images- display, menu boards, flyers, printed menus, in-store decore, billboard or transet advertising, or online menu for delivery and pick-up orders. A moderately-priced consumer model or so-called profession model may do the job.
Camera aside for a moment. Let's examine food and beverage photogahy. Basically, you want the images be appeal to the appetite of the prospective customers. The most important part of that is food styling and lighting. A good chef or even an experienced short-order cook knows how to "make a plate" or preset a food product. Some make tasty food but have no eye for aesthetics. Food does necesserally need to be "faked" or overly cosmetic but there are tricks of the trade to make it more photogenic. The treatment or cooking procedure depends on the item.
Lighting1 That can be simple but it needs to be addressed. A setup can be designed whereby it can be easily accessed and operated in a minimal space. I continuous or flash ligh source in a medium-sized softbox plus a couple of reflectors can suffice for many kinds of food layouts. It is important to render texture and show freshness without excessive glare.
If the OP would tell me what the menu is like and the usage of the images, I can make more specific recommendations.
I do most of my food shots, nowadays, with a digitally converted Mamiy RZ67 and a special tilt lens- also a custom-made conversion. But, don't knock on the cell phone camera. I shot my wife's favorite veggies in a woc on the stove- with a lightbulb in the range hood and my trusty Samsung phone.
Greetings! br br I do food photograhy profession... (