whatsapp voice volume messages

I'm not sure if my iPhone doesn't have this feature or if all the iPhones don't have this functionality. I'm a new iPhone user. I used Android until this time. And basically, I can't adjust the volume of the earpiece speaker while I am listening voice messages on Whatsapp through the earpiece speaker. Because Whatsapp has the function to hear voice messages directly via an earpiece speaker when approaching the ear. But I can't adjust the volume. I tried to adjust the volume on cellular (normal) calls, and it worked. But it doesn't work on Whatsapp messages and it is the same on Telegram. Android has this feature. Is there a fix for this? Or is it absent in the first place?