Does the server reads specific rows from spam numbers DB or the whole database?
In this PIR model the server runtime is O(n) where n is the number of rows.
To keep it practical, we do support sharding the database. Client leaks a few bits of hashed query to pick the right shard, where we process the entire shard. There is a inherent privacy-performance tradeoff: less shards = less leakage vs more shards = better performance & less privacy.
Run SHA256 on the keyword, truncate the hash and take the modulus with number of shards.