Hi @Anonymous,
You can use the addcolumn function in the item property of the gallery to add numeric values to the items.
For example,
Your items property could be (assuming Production is the datasource)
SortByColumns(AddColumns( Production, "PhaseSortOrder", If(Phase = "PhaseA" , 1, If(Phase = "PhaseB", 2), If(Phase = "Phase3", 3))), "PhaseSortOrder", Ascending)
Please let me know if this helps and mark this reply as the solution. Thanks!