What is the meaning of this sentences?
Perceptions of threat are hypothesized to be influenced by one’s own vulnerability, and thus to be greater among those individuals who are experiencing more difficult economic conditions or vulnerability.
This is not a particular phrase. In this context, "thus" means the same as "therefore".
Here is a paraphrase.
Perceptions of threat are hypothesized to be influenced by one’s own vulnerability, and therefore perceptions of threat are greater among those individuals who are experiencing more difficult economic conditions or vulnerability.