while grinding for the cell phone might be annoying, I think there might be some reason why the angler quests are limited to one quest a day. I might be wrong, but my idea is, it's to try to discourage players from trying to do things like marathoning the 200 fishing quest achievements. fishing is useful, but usually not very amusing. if a player decides to focus on going back-and-forth 200 times in a row between lakes and the angler, it could just outright kill any zeal the player had for the game. or so I think. because that would be just crazy boring and monotonous.
but if you spread out fishing quests more, they're much less bad. and the fishing quest achievements counter carries over to other playthroughs, so if you spread it out to multiple, even the 200 quests can be done eventually, without being all that boring. but if you try to marathon it... ...well, there are people who try it, it is up to them how they play. so, from that regards, it -could- be enabled to do as many quests a day the player wants, but I would be afraid it would increase the amount of people complaining about "fishing is super boring" because they tried to marathon the 200 quests.