"Phebe is either the dau. of Solomon Gee III & Elizabeth Bruce or Leuman Gee & Catherine Bruce. It's unclear which, but she does name a son, Solomon Gee Smith, which suggests, that Solomon III was her father. Additionally, Solomon III, in the 1800 NH Census, has a female under 10yrs old. Phebe fits here. In the 1810 VT Census he has a female 10 to 15yrs old. Again, Phebe fits here. By 1820, she is married & living with John Smith in Lunenburg.
Leuman is much more difficult to deal with, as he died in early to mid 1805 in Lunenburg. The 1800 NH Census for him is not very helpful as the number of girls does NOT add up. There should be more, but there isn't. However, if we take into consideration that Leuman & Catherine had a dau., Catherine "Caty" Gee, in July, 1800, does it seems plausible that they had a dau. 10 months earlier, in Sept. of 1799? That is a very short turn around.
Another contributor has stated that dna proves that Phebe is a dau. of Leuman, but given that Leuman & Solomon were brothers & married sisters, & given that they were 3rd, 4th or 5th great grandparents to us today, it seems that it would be very difficult to differentiate the two couples."  - From FamilySearch contributor, JPL2.
↑Phebe Gee in FamiySearch.org, Family Tree, profile KCFN-CTT.
"United States Census, 1850," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:MC2Z-4BQ : 12 April 2016), Phebe Smith in household of John Smith, Concord, Essex, Vermont, United States; citing family 15, NARA microfilm publication M432 (Washington, D.C.: National Archives and Records Administration, n.d.).
"United States Census, 1880," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:M8WC-75B : 15 July 2017), Phebe T Smith in entry for John Smith, 1880; citing enumeration district ED 91, sheet 325A, NARA microfilm publication T9 (Washington D.C.: National Archives and Records Administration, n.d), roll 1342; FHL microfilm 1,255,342.
"Vermont, Town Clerk, Vital and Town Records, 1732-2005," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:QPQG-93CK : 29 November 2018), Phebe Smith, 25 Oct 1882; citing Death, Concord, Essex, Vermont, United States, various town clerks and records divisions, Vermont; FHL microfilm 005488144.