Looking at this simplistically, if you're outside DODNE and the controller merely says "Cleared approach
" without any altitude assignments, then technically you should begin your climb to 3000 in the vicinity of DODNE.
One that you'll still occasionally hear is simply, "Cleared approach to the OVERTHERE airport."
As a matter of good form, whenever I get the simple "Cleared approach," I always tell them what approach I'll fly, but there's no requirement to do so.
You're expected to maintain the last assigned altitude until you're on the approach, but oftentimes they will even say so, as in, "Maintain 2000 until on a published segment of the approach, cleared approach, Natchez." This example may be additionally confusing since the controller doesn't specify an approach, allowing you to start it from RUCBO or continue all the way to the HEZ VOR and begin any approach (including this one) that transitions from there.
Think of it as a combination of a block altitude assignment and an unspecified "Cleared approach."