Some do recommend that you should have somewhere to house it, like a small bottle, jar, or ring. This is partly where the “genie (jinn) in a bottle” legends come from. Some people use body parts like knuckles, toes, elbows, etc. This is to anchor your entity to the physical/material realm.
Here’s an idea:
House your servitor inside a cellphone, tablet, or USB flash drive.
I have one anchored to a scroll inside a tiny bottle. And a sigil for her. Then there are others that say you should structure a servitor without using a sigil.