Fix PHONE.csv import duplicate constraint error

- Implement upsert logic in import_phone() function
- Check for existing (id, phone) combinations before insert
- Track duplicates within CSV to skip gracefully
- Update existing records instead of failing on duplicates
- Add detailed statistics: inserted, updated, skipped counts
- Align with upsert pattern used in other import functions
- Add documentation in docs/PHONE_IMPORT_FIX.md

Fixes: UNIQUE constraint failed: phone.id, phone.phone error
when re-importing or uploading CSV with duplicate entries

data-import/gruplkup_06de2a1b-c70c-4ff3-9b4c-4332efb97f2d.csv

@@ -0,0 +1,25 @@
+Code,Description,Title
+1,client party,
+1A,client's attorney,
+2,opposing party,
+2A,opposing attorney,
+AC,attorney-commercial,Attorney at Law
+ACO,attorney-civil only,Attorney at Law
+AD,attorney-defense,Attorney at Law
+AFO,attorney-family only,Attorney at Law
+AG,attorney-general,Attorney at Law
+BUS,business related,
+COC,Clerk of Court,
+EXP,expert witness,
+FCC,Commissioner,Family Court Commissioner
+JUDG,Judge,
+LGLA,legal assistant,Legal Assistant
+OBSLT,obsolete entry,Attorney at Law
+PA,plan administrator,Plan Administrator
+PAR,paralegal,Paralegal
+PEN,pension subect,
+PER,personal,
+QDRO,QDRO subject,
+SPOUS,subject's spouse,
+SUB,subject of report,
+VOC,vocational consult.,