If you don't know or haven't checked out the basic mechanism of blockage, here it is:

The tumor spreads to nearby lymph nodes.
Small-intestinal carcinoid tumors commonly spread through lymphatic vessels to the mesenteric lymph nodes.
The lymph nodes can become enlarged and contain tumor cells.
These deposits can form a mass in the mesentery, the tissue that supports the intestines.
A desmoplastic reaction develops.
This is particularly characteristic of small-bowel neuroendocrine tumors. The tumor can trigger production of a lot of fibrous, scar-like tissue around the tumor and lymph-node deposits.
The mesentery becomes stiff and contracts.
The fibrosis can pull on and distort the nearby intestine and its blood vessels. This may cause the bowel to kink, narrow, or become fixed in an abnormal position.
The result can be partial or complete obstruction.
The blockage isn't necessarily because a lymph node is simply "plugging" the intestinal opening. More often, the tumor + enlarged lymph nodes + surrounding fibrosis distort and constrict the bowel from the outside.

Why this can be confusing

A person can have a fairly small primary carcinoid tumor but significant bowel problems because the secondary effects in the mesentery can be much more extensive than the original tumor.

Symptoms of obstruction can include cramping abdominal pain, bloating/distension, nausea, vomiting, and difficulty passing stool or gas. A complete obstruction can be an emergency.