From Nessus, it should support POSIX/PCRE regex. I am trying to match Malaysia phone numbers and it is working on regex101, but using the same regex in nessus audit fails.

<item>
  type           : FILE_CONTENT_CHECK
  description    : "Checks for phone numbers"
  file_extension : "pdf" | "doc" | "xls" | "xlsx" | "xlsm" | "xlsb" | "xml" | "xltx" | "xltm" | "docx" | "docm" | "dotx" | "dot"
  regex          : "(+?6?01[0-46-9]|+?6?0[3-7]|+?6?08[0-9])-?[0-9]{7,8}"
  expect         : "FAX" | "Fax" | "Phone" | "PHONE" | "CELL" | "Cell" | "Mobile" | "MOBILE" | "Tel" | "Tel No." | "MobileNo"
  max_size       : "2k"
</item>