By the 1900s, most phones were being produced with enclosed mechanics. This example was made by Kristian Kirks for the Jydsk (Jutland) Telephone Company c1920. It was later converted for dial working, though experts will note that the dial label is from KTAS, not JTAS, but this is more authentic than the British dial fitted when I acquired this. In fact, the dial is a recent addition when these phones were sold in the 1970s as ‘antiques’. Originally the phone was designed for magneto PBXs and the red button controlled connection of a common magneto supply to the line for ringing the operator, while the other provided a bell and microphone cut-off. This is why the body is so much smaller than the Corporation Set, since no magneto is needed. The handset looks like the characteristic Ericsson type, but this is only superficial. The carbon microphone inside was quite different to avoid Ericsson’s patent.
More information on this type of phone is available here.