Is my phone 4G

It depends on your carrier whether you have 4G or not.

iPhone 6s Plus:

A1634: LTE (Bands 1, 2, 3, 4, 5, 7, 8, 12, 13, 17, 18, 19, 20, 25, 26, 27, 28, 29, 30), TD-LTE (Bands 38, 39, 40, 41), TD-SCDMA 1900 (F), 2000 (A), UMTS/HSPA+/DC-HSDPA (850, 900, 1700/2100, 1900, 2100 MHz), GSM/EDGE (850, 900, 1800, 1900 MHz) A1687: LTE (Bands 1, 2, 3, 4, 5, 7, 8, 12, 13, 17, 18, 19, 20, 25, 26, 27, 28, 29), TD-LTE (Bands 38, 39, 40, 41), TD-SCDMA 1900 (F), 2000 (A), CDMA EV-DO Rev. A (800, 1700/2100, 1900, 2100 MHz), UMTS/HSPA+/DC-HSDPA (850, 900, 1700/2100, 1900, 2100 MHz), GSM/EDGE (850, 900, 1800, 1900 MHz) A1699: FDD-LTE (1, 2, 3, 4, 5, 7, 8, 12, 13, 17, 18, 19, 20, 25, 26, 27, 28, 29), TD-LTE (38, 39, 40, 41), TD-SCDMA 1900 (F), 2000 (A), CDMA EV-DO Rev. A (800, 1700/2100, 1900, 2100 MHz), UMTS(WCDMA)/HSPA+/DC-HSDPA (850, 900, 1700/2100, 1900, 2100 MHz), GSM/EDGE (850, 900, 1800, 1900 MHz)

Yes, it has 4G capability.