I agree. My cab had no cup holders. I am an avid bicyclist so I took a couple water bottle holders that are normally mounted on a bicycle and I bolted them to the dash. They work great. Most often I drink water so I just keep a bicycle water bottle in there. But, when the Mrs. makes us smoothies my large plastic glasses also fit in pretty well. I don't drink coffee but I imagine a coffee tumbler would fit fine too.
Now, how about where to put the dang cell phone? I found a small mesh thing in the cell phone accessory area. I think it's made to hold a cell phone. But, it had some goofy clip kind of thing to hook it into the dash vent. I tossed that. I put a 3M Command hook thing on the dash and I hook the bag on that. When the phone is plugged into the charger I just put the phone in upside down so the cord sticks out the top. That's for Mrs' phone. I put a Ram X Grip mount on the overhead console on my side and I keep my phone on that. https://www.rammount.com/products/xgrip/un7_learn
'03 Freightliner FL112, 295" wheel base, with '03 United Specialties 26' living quarters, single screw, Cat C12 430 h/p 1650 torque, Eaton 10speed , 3.42 rear axle ratio