Dimensional Box

A box you can store stuff in, as there is a limit to how many items you can carry at a time. There are a few physical boxes before Alphys upgrades your phone. Onward, your phone has two dimensional boxes where you are able to use the box function from your phone. If the player is doing a Genocide Route then Alphys does not show up to upgrade their phone, but 3 more boxes are placed to compensate for this.

Box Locations
Snowdin Forest Snowdin Waterfall MTT Resort (Genocide Route) New Home (Genocide Route)
 * Located on the road just after you meet Sans and Papyrus for the first time.
 * Located in front of the Snowed Inn and Shop.
 * Located outside of Gerson's shop
 * Located to the right just after entering.
 * Located right outside the house, in front of the right window.
 * Located in Last Corridor, beside the save point.