Conversion from varchar2 to timestamp
According to ISO 8601 T is the time designator.
You need to use a constant "T" in your date format mask.

And your time stamp contains timezone so you need to use TO_TIMESTAMP_TZ function to achieve this.

SQL&gt; select to_timestamp_tz('2017-02-14T18:04:34.988+00:00',' YYYY-MM-DD"T"HH24:MI:SS.FF TZH:TZM') from dual;

TO_TIMESTAMP_TZ('2017-02-14T18:04:34.988+00:00','YYYY-MM-DD"T"HH24:MI:SS.FF
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14-FEB-17 06.04.34.988000000 PM +00:00


Documentation:TO_TIMESTAMP_TZ