I guess You mean Flicker or flashing?

You don't need any special pass through cable, You can use a VGA cable as long as one end is male and the other female.
Seems a bit odd if only in the console. Maybe try some other games, especially ones that use glide. Quake and Quake 2 use opengl, or minigl in the case of the voodoo card.
Also You could try Tomb raider 3dfx version in dos.

From what I understand, the output on some voodoo 1 and 2s can be pretty noisy. I've seen reports of vertical lines, horizontal lines, and have experienced scrolling lines at a 45 degree angle on one of my voodoo 2 cards. These are usually like "shadow lines" or bands of alternating opacity.

Are you on an analog or digital monitor? Try a CRT if you are using an LCD. Or try adjusting the vertical and horizontal clock signal on the digital monitor (try auto-adjust first). Other users have used a low pass filter to resolve their issues. I've also seen someone report that a VGA splitter/signal booster box resolved their issue.

Post a capture or video from your phone if possible. Maybe these examples can help you describe what's happening.

Example of horizontal noise: https://www.youtube.com/watch?v=Qk0eCpgo6_c
Example of vertical banding: download/file.php?id=45224&mode=view
Example of diagonal banding: download/file.php?id=129066&mode=view
Example of snow/glitches (voodoo 3 issue): https://www.youtube.com/watch?v=zVBMC8194ps