We use phosphor bronze strings for some of the lower notes on our dulcimers because of the tone they produce. In certain spots, phosphor bronze provides a slightly clearer and richer tone than steel does. However, it is a softer material and more prone to work-hardening, which means that phosphor bronze strings break more often than steel strings.
It can be really frustrating to experience a spate of string breakages, especially if it gets to the point where you can barely get a new string on before it breaks! There's nothing less fun than putting on your fourth string in a row and cringing in anticipation of the BANG and the flailing string end. There's not a great answer to why this happens sometimes but not all the time, and to some people but not others, but there is hope!
It is totally fine to replace your problem PB string with the equivalent diameter in steel. The tone will be slightly different, but the steel string will be much less likely to break. Depending on your ear and your priorities, it might be the best decision you ever made, or you might realize the more frequent breakage was actually a worthwhile tradeoff for the tone.
If you've tried this solution, what did you think? Did you stick with it or did you go back to PB?