Each business has two upgrade tracks:

• Level upgrades raise that business's earn rate per dice roll. Each business has a fixed maximum level.
• Phase upgrades happen when you reach max level. The business is replaced by a bigger version (for example Coffee Truck → Coffee Hut → Coffee Shop), which then starts leveling up from L1 again with a higher base earn rate.

When you reach max level you can choose to phase up or sell the business — the sell pop-up shows your current sell offer.