Does the concentration on the phase prevents cpncentrarion on spells? If so, using the class featurea actually make you less versatile than the sorcerer already is with ots limited spells know.
Also, having to spend a action to enter a phase seems a bit much. Compare it to barbarian rage granting resistance and vpnus damage pretty much onntha same way, it only requires a bonus action to enter, and while it does have a 'restriction' on to keep the effect going, it also doesn't end on beeing hit... i say make it a bonus action.
Otherwise really cool idea, keep imagening an astrologist "predicting" peoples deaths before killing them with fire/cold/force damage
Also, having to spend a action to enter a phase seems a bit much. Compare it to barbarian rage granting resistance and vpnus damage pretty much onntha same way, it only requires a bonus action to enter, and while it does have a 'restriction' on to keep the effect going, it also doesn't end on beeing hit... i say make it a bonus action.
Otherwise really cool idea, keep imagening an astrologist "predicting" peoples deaths before killing them with fire/cold/force damage