Yup. Media apps like YouTube, Spotify, Netflix, etc. should use both speakers. Speakerphone (calls, voicemail, VoIP call apps and IM voice calls) use only one speaker.
I just had to call to refill a prescription. Used speaker phone on the automatic voice the pharmacy has, and both worked. I put the bottom against me as I entered the bottle number and it was more quiet. Held my Note 9 away from me and it was louder. Held close to my ear to check the speakers and sound came out of both.