He using them both in that panel but he was not phasing and sniping at the same time, he was doing something completely different.
exactly Obito can either use:
- Both Kamui at the same time to to create Space portal
- Both Kamui separately as he did to slip in Kaguya's dimenssion unnoticed.
Obito can also uses any attack bar Kamui while staying itangible. Konan stated that Obito need to become tangible to warp someone or himself... I know it may be due to both abilities come from same eye, but it could be asbolute rule for Kamui use while being tangible so no.
The manga has never shown or stated Kamui user sniping someone while staing itangible so as far as manga goes Kamui user can not do that. While it may seem possible, Kishi would nerf it anyway or simple make failsafe to state it is impossible so Kamui user can be beaten.