Da, mam. U menia fsio otlichno. (literally: I'm excellent if you want that rather than just fine)
The unstressed O sounds like a relaxed A or a schwa (the unstressed vowel typical for English, the one you hear in the word typical, or language, or August, etc.) Likewise, the unstressed E in menia is relaxed and close to I.
In menia vsio, those IA and IO aren't really IA and IO. This is an example of palatalization which is very hard for foreigners to capture.
A translation into Cyrillic Russian if you decide to include it in the text of the play:
Да, мам. У меня всё отлично.
If you decide to include a transcription, write vsio instead of fsio (the latter would look ridiculous).