You’d be forgiven if you had trouble keeping track of all the septuagenarian (or darn close) WASPs in Paul Osborn’s 1939 Broadway play “Morning’s at Seven,” for the same reason the splendid older actors who have helped dust the show off for a run at the Phoenix Theatre seemed to mistake each other during opening night’s run: There are just so darn many of them.

It helps (though it is a bit annoying after a while) that Osborn’s script has the characters repeating their names to each other throughout the three-act play.

But there’s no confusion about this fact: Phoenix Theatre’s “Morning’s at Seven” is a charmer. It’s getting considerable, well-deserved attention for the fact that it’s making good use of several veteran Valley actors and actresses — Jack Ritschel, Peggy Lord Chilton and Betsy Beard, namely — in a play that proves there’s no arthritis in their funnybones. They don’t navigate their roles independently so much as band together to put on a show with as much group love as the hot-flashin’ gals over at “Menopause — The Musical.”

The play’s plot is both simple and strange. The four aging Gibb sisters have lived closely together in a small Midwestern town for most of their lives. Three are married (one, to an insensitive intellectual of a man who forbade his wife from visiting her simpleton sisters) and nosy Arry (played by Beard) who has never married, instead sharing a house with a sister and her husband. Just as the 40-year-old son of one of the couples comes home to introduce his girlfriend (“You don’t suppose she’s a cripple or somethin’?,” Arry asks), the old folks decide they’re due for some life-changes themselves.

Set designer Gregory Jaye has built a beautiful set here, which is welcome in a play that never leaves the backyards of two Gibb sisters’ neighboring houses. The feeling of seclusive family living is made more apparent by the transparent walls of the houses — revealing goings-on for all to see.

Though our attention belongs with the sisters and their hubbies, it’s worth noting the performance of Chris Vaglio, a resident PT actor who was positively crummy in the company’s “Private Lives” earlier in the season. Here, as the son who’s come home, he’s a Clark Kent to the Superman-size British ego of his former disaster; a consummate mama’s boy, Vaglio’s Homer squirms and stutters at the thought of showing affection toward his girl (played by Robyn Allen) in front of the family. But just as the elder folks make changes, so does Homer — and Vaglio steers his character with moments of comic brilliance.