I hope you are referring to the below table from S29GL128P datasheet (https://www.cypress.com/file/219926/download).
Each memory location in S29GL128P device has size of 2 bytes (16 bits).
As per the above table, the number of address locations in one sector is 65536 (0000h - FFFFh).
Total number of bytes in one sector = 65536 x 2 = 131072 bytes = 128KBytes.
I hope the above information answers your query. Please let me know, if you have any other related queries.
Thanks and Regards,