Exhibit 5.1



                    RUSKIN, MOSCOU, EVANS & FALTISCHEK, P.C.
                              170 Old Country Road
                            Mineola, New York 11505
                                 (516) 663-6600


                                        July 1, 1996




Periphonics Corporation
4000 Veterans Memorial Highway
Bohemia, NY  11716

                           Re:  Periphonics Corporation

Gentlemen:

     We have acted as counsel to Periphonics Corporation, a Delaware corporation
(the "Company"),  in connection with its filing of a Registration Statement (the
"Registration  Statement")  on Form S-3 with  respect  to  39,125  shares of the
Company's  Common  Stock to be sold by  Ascom  Telecommunications  Limited  (the
"Selling Stockholder"). In connection therewith, we have examined such corporate
records,  certificates  and documents as we deemed  necessary for the purpose of
this opinion, including,  without limitation, the Company's Amended and Restated
Certificate  of  Incorporation  and Amended and Restated  By-Laws.  Based on our
examination,  we advise you that, in our opinion, the Common Stock to be sold by
the  Selling   Stockholder   is  duly  and  validly   issued,   fully  paid  and
non-assessable.

     We hereby  consent  to the  filing of this  opinion  as an  exhibit  to the
Registration Statement and to the reference to our firm under the caption "Legal
Matters" in the Prospectus constituting a part of the Registration Statement.


                               Very truly yours,


                               /s/ Ruskin, Moscou, Evans & Faltischek, P.C.
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                               RUSKIN, MOSCOU, EVANS & FALTISCHEK, P.C.