Modes of portrayal
When you portray an NPC, you can speak in their voice, in first-person ("I… just don't know if I can keep… doing this"). Or, you can summarize what they say and how they say it, in third-person ("She tears up and says she can't keep doing this—it's awkward").
Speaking in an NPC's voice tends to be more immersive and engaging than just summarizing their words. It prompts players to respond in kind, speaking in the voice of their PCs. It allows you to show instead of tell. And it can be an awful lot of fun.
Summarizing an NPC's words is often easier to do. It doesn't require skill in acting. It's easier to correct yourself. It often takes less time to summarize a conversation than to play it out. You can be more intentional about the info you share and the GM moves you make.
In practice, you'll often switch between modes. You might start in third-person but deliver a key line in an NPC's voice. You might start in first-person, then zoom out to summarize their tale. You might describe a conversation that involves multiple NPCs, but punctuate it with a few key lines in specific voices.
Try to be mindful and intentional about how you use modes of portrayal. Pick and choose based on the needs of the scene, the pacing of the session, and the preferences of your players.
Challenge yourself! If your instinct is to always summarize what NPCs say, try a bit of first-personal portrayal. If you find that you always speak in-character, try summarizing conversations instead. GMing is a practice, and you only get better at things you try!