The total number of index pages scanned during entire vacuum will depend on number
of index scans that happens.
In order to extrapolate percent complete for phase two(index scan) we need number of index scans * total index pages.
The number of index scans can vary from 1 to n (n depending on maintenance_work_mem)
Summarizing suggestions in previous mails, following information can be reported
Phase 1.heap pages scanned / total heap pages
Phase 2.index pages scanned / total index pages (across all indexes)
Phase 3.count of heap pages vacuumed
Additional info like number of index scans so far, number of dead tuples being vacuumed in one batch can also be provided.
A combined estimate for vacuum percent complete can be provided by summing up heap pages scanned, index pages scanned against total heap pages, total index pages * number of index scans.