Theory:

But no one descended to the Traveller;
No head from the leaf-fringed sill
Leaned over and looked into his grey eyes,
Where he stood perplexed and still.
But only a host of phantom listeners
That dwelt in the lone house then
Stood listening in the quiet of the moonlight
To that voice from the world of men:
Stood thronging the faint moonbeams on the dark stair,
That goes down to the empty hall,
Hearkening in an air stirred and shaken
By the lonely Traveller’s call.
Explanation:

No one came to open the door, even though the traveller knocking the door again and again. The traveller couldn't see anyone even on the window sill above. He expected someone to lean over the window sill, which was full of leaves and look into his eyes that was grey. Here the poet says the traveller’s eyes being “grey" which portrays his emotions. The traveller was expecting someone to help him. The traveller was confused and still standing there.

Since no one is opening the door, the poet says the only possible listeners are phantoms or ghosts that live in that abandoned house. Hence, the house remains abandoned the traveller says that the phantoms or ghosts are the only inhabitants of the house. The ghosts stood listening to the voice of the traveller from the world of human beings. They go within the empty hall and take to the stairs as any normal Human beings would. These ghostly forms do not make contact with their world. They are helpless to reply to the “Traveller’s call,” although they can hear it. The air around them is moved and swayed by the sounds made by the alone travellers call.

Meaning of difficult words:

 Numbers Word Meanings 1. Leaf-fringed An outer edge of leaves. 2. Phantom Ghosts. 3. Hearkening Listening.
Reference:

The rhyming words from the lines $$8$$-$$19$$ are:
1. Sill- Still
2. Then - Men
3. Hall - Call
Reference:
State Council of Educational Research and Training (2019). Term-1 English Standard-7. The Listeners by Walter de la Mare (pp. 42). Published by the Tamil Nadu Textbook and Educational Services Corporation.