Many languages have sounds that are very hard to pronounce to certain speakers. For example the french "R" sound is hard for English speakers. What if we have a language that accepts many variations of a word so that it's still accepted even if it sounds a little different? For example, Japanese phonology does not distinguish between L and R. This video shows how incredible it is. I think this is a similar concept to how languages can change how many things you can notice, even colors can be hard to distinguish if you don't have a word for it. But if you're coming from a language that does distinguish between the sounds, it will be easier for you to pronounce words of a language that doesn't distinguish it. I think that the Japanese L/R sound is easy because they don't care which one you pronounce, it sounds the same to them.
However, I know it might cause the language phonology to be too simple, which will cause very long words. I have not studied every single language in the world. But is really that bad if we are to create this "combined phonology?"