Different markets in India have different working days. While one market in a city will be closed on Mondays or Tuesdays, other markets will be open. While another market is closed on Sunday, other markets will be open on Sunday. Also, while some market may be open, some types of stores may be closed on a certain day in that market but open even on the days when the market is closed.

Like open market days, shop hours can be all over the place too. Generally, I never head to a shop before 11.30 a.m. or after 7 p.m. unless I've talked to the store staff to make sure the person/persons I need to deal with will be there. Otherwise it's a gamble. It's not uncommon for stores to be closed "randomly" too -- either for part or the whole of a day -- for family occassions/chores, personal religious holidays/ceremonies, etc.

If he goes back to the store when it's open, more likely than not they'll eventually find his phone. Also, remember that at a lot of stores in India that say they'll do the work for you, they'll send it to another shop/location to get the work done and then have to bring it or wait for it to be brought back. They don't usually tell you that, but people who know India are not surprised that's how it often works.

If you can tell me where the shop was located that would be helpful.

Only very well-informed locals that know a marketplace or store would really know when a particular marketplace, store or type of store is likely to be open or closed.