I can only speak as a plumber, but over the years it has always been helpful when customers can answer two questions: "What part of the house is affected?", and " What plumbing is affected in those areas?". Then we can get down to if its coming up in the tub or just the toilet. Too many times homeowners want to just say that bathroom is backing up. Well they are standing right there. Of course this is an excellent description for them, but for us the plumber, we need some more info to get the right equipment in the truck and out to your problem.
The best way to explain a sewer problem to a plumber over the phone is to describe the symptoms clearly and provide as much context as possible. Mention specific details like unusual odors, slow drains, gurgling sounds, or backups, and note whether these issues affect one fixture or multiple areas. If possible, share what's been tried already, like plunging or using a drain cleaner, and whether there's been recent heavy rain or construction nearby. This approach works because it gives the plumber a clear picture of the problem before arriving, allowing them to prepare with the right tools and equipment. It saves time and reduces the need for repeat visits since they can better anticipate whether it's a localized clog or a larger sewer line issue. Direct, detailed communication is the key to faster and more effective solutions.