In order to view all the numbers associated with a certain contact, drag the contact to the call or SMS icon, and hover above it without dropping. A pop-up window with all of its numbers will appear. There, you can choose which number you'd like to use in order to complete the selected action, as well as setting one of the numbers as the default by tapping to its left - the default number is the one with the green plug icon to its left.
Another suggestion: you can try testing our expandable action icons. Go to drupe settings > Dots > Advanced > check Expand Actions (Beta). What this will do, is display different sub-actions when you drag a contact to a certain icon. If your selected contact has more than one phone number, dragging it to the call / SMS action icon will have "More numbers" as one of the expanded options. Try it, you might like it!