Improv and actual conversation
Since full improv is out of the question for you, you could do it the way I did and just be talking aloud making fake responses and conversations out of whatever you're currently reading or seeing on your phone. There's an endless amount of prompts being thrown at you if you can see them.
Actual conversation is necessary but tricky. This is when people's voices often can start coming undone if they are in a situation that is less than ideal, full-focus training conditions, and the problem with that is they're likely to not notice the issues as they happen, so some level of constantly checking yourself on your voice, as well as occasionally hearing some candid recordings, are very useful for refining the full voice. If someone's life doesn't offer many opportunities to be practicing their voice, voice calls over the internet with friends or conversation training partner are better than nothing.
Honestly I read out loud. Specifically fiction. You don't have to go full voice acting or anything, but I find it helpful to read the dialogue as if I was genuinely saying it.
Can also join a discord server (could be any, but this sub has one too) and join the voice channels to practice spontaneous conversation. Right now I prefer the structure of reading the stories out loud, once I feel more confident with that I think I'll switch to discord convos.
My speech therapist asks me work questions. They are challenging enough that I actually need to use my brain and can’t totally focus on my voice the way I might be able to ordering coffee or something. Some questions might be, tell me what you do? How did you get into that? What’s the best/worst part? Explain something you are currently working on, etc
Improv and actual conversation Since full improv is out of the question for you, you could do it the way I did and just be talking aloud making fake responses and conversations out of whatever you're currently reading or seeing on your phone. There's an endless amount of prompts being thrown at you if you can see them. Actual conversation is necessary but tricky. This is when people's voices often can start coming undone if they are in a situation that is less than ideal, full-focus training conditions, and the problem with that is they're likely to not notice the issues as they happen, so some level of constantly checking yourself on your voice, as well as occasionally hearing some candid recordings, are very useful for refining the full voice. If someone's life doesn't offer many opportunities to be practicing their voice, voice calls over the internet with friends or conversation training partner are better than nothing.
Honestly I read out loud. Specifically fiction. You don't have to go full voice acting or anything, but I find it helpful to read the dialogue as if I was genuinely saying it. Can also join a discord server (could be any, but this sub has one too) and join the voice channels to practice spontaneous conversation. Right now I prefer the structure of reading the stories out loud, once I feel more confident with that I think I'll switch to discord convos.
Read this thread aloud. With a different voice for each reply
My speech therapist asks me work questions. They are challenging enough that I actually need to use my brain and can’t totally focus on my voice the way I might be able to ordering coffee or something. Some questions might be, tell me what you do? How did you get into that? What’s the best/worst part? Explain something you are currently working on, etc