Solution 1:

I know no authoritative reference for this. In educated and uneducated speech I have heard calm with no l as in harm, calm with as strong l, and variants inbetween. All may be considered correct.

Solution 2:

To understand the potential for variation, I recommend that you start out saying "caw". During this, your tongue will naturally stay at or near the bottom of your mouth.

Now say "caw-m". Your tongue stays at the bottom of your mouth as your lips close for the "mm" sound.

Now say "call" ("caw - ll"). To make the L sound your tongue has to move from the bottom of your mouth to touching the roof of your mouth, just behind your upper front teeth.

Now move to "caw - l - m" (as three connected but distinct, slow sounds). Moving from the L sound to the M sound,your lips close and your tongue moves back to the center of your mouth.

Finally, start speeding up the pronunciation, trying to make the L and M parts closer together and less distinct. At some point you will notice that you don't have to actually touch your tongue to the roof of your mouth; just having it in the middle of the mouth produces a "semi-L" that is distinct from the "no-L" sound when your tongue stays low, and this is what is indicated with the /kȯ(l)m/ pronunciation option.

So, depending on how quickly and how carefully you are trying to say it, you may end up almost anywhere in the spectrum of "no-L" to "full-L" pronunciation.