According to the docs here on upgradeability, the PhiNFT1155 contracts use the UUPS upgradeability pattern and can be upgraded by the owner.
Currently though, it is not possible to upgrade them since msg.sender has to be the owner, which would be the factory contract and the factory contract does not have a mechanism to upgrade contracts, i.e., call the upgrade functionality in the UUPSUpgradeable contract inherited by PhiNFT1155.
Its not clear how the factory contract could have and support multiple implementation contracts of PhiNFT1155 (since many contracts can be created through function createArt() in the PhiFactory contract). If upgradeability needs to be supported, introduce a proxy for each PhiNFT1155 contract deployed and a mechanism upgrade it through the factory. If not, correct the documentation. 
