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Our DM is super strict so I wanted to know if I could talk to something on the inside side of a wall of force spell if you use the sphere option.
An Invisible wall of force springs into existence at a point you choose within range. [...] Nothing can physically pass through the wall. [...]
Because it says nothing physical can pass through the wall, I wasn’t sure if he'd consider sound 'physical'.
It is dangerous to try and approach D&D magic with a physics interpretation. There is nothing in the spell that specifically prohibits communication, which would be a fairly common activity. It is so common that it would almost certainly be called out in the rules.
A DM is always free of course, to interpret the rules for their table (that is a large and expected part of their job), but trying to adjudicate the magic posited within the game with physics will almost certainly end in failure. Half Orcs and Half-Elves would be very unlikely given a knowledge of modern biology, for instance. Dragons would not be able to fly given their weight and surface area. And so forth.
It is magic, and it does what it does.
In D&D 5th edition, two principles which apply when adjudicating rules:
Since there is no rule specifying otherwise, then, officially, adjudicating whether sound is "physical" for the purposes of a wall of force is entirely up to the DM.
However, if you want to be able to talk to someone you trap within a hemispherical wall of force, simply create the wall one inch off the ground. The spell allows the wall to be free-floating, and the gap would allow speech.
Additionally, unless the dungeon floor is also a wall of force, it's not perfect; it's going to have gaps and cracks that would allow sound. It may also be possible to hear someone through the connecting stone floor if you shout loud enough (imagine listening to someone through a wall).
If your DM considers vibration to be blocked by a Wall of Force, then it will naturally block sound. However, unless the listener is completely enclosed by the spell, you may be able to communicate by relying on surfaces/spaces (stone walls, wooden floor, an air gap above or below them, etc). If the DM rules that the other surfaces dampen the sound too much, you may be able to establish communication by loudly knocking on those surfaces, if you share some sort of pre-existing code (Morse, a thieves cant, ...).
I'm assuming whatever is on the other side of the Wall of Force cannot see you. If they can, then you can use pantomime or writing to establish a tap-code for them to use (or sidestep the issue entirely if they have the means to write back).
If they are completely enclosed (i.e. the Wall is a sphere) then I'd say there is no way to communicate with them via sound without additional magic.
