It would be possible but difficult. The problem is that apple trees need a dormant period over winter. It will need to freeze and stay cold. In a pot above the soil and especially on a porch, the pot will freeze and then thaw, freeze and then thaw repeatedly over winter. All this won’t allow the plant to enter the dormancy it needs over the winter and this will kill it. If you want to attempt this then you need to, in the fall (like late October), take the entire planter and sink it up to the rim in the ground for the winter…preferably in a sheltered location out of the north and west wind. This will keep the soil frozen and let the tree follow its natural growth cycle. It should be left there until late March/Early April when it can be moved back to the porch for the summer. In addition to being large enough for the tree, the planter you choose will have to be made of a material that won’t shatter from the cold over winter…high quality ceramic most likely.