It has a alot of zippered compartments. I keep my credit cards in my wallet. I never have put them anywhere else except my wallet. Because when I go shopping I just take my wallet with me and not my purse. I love this purse! I like all the different compartments and also the feel of the leather. This was a great buy for me. I guess you could use it for credit cards but in my opinion I wouldn't take the risk.

Will one of the outside pockets hold my samsung S9+ cellphone?

The front pocket holds my S10e easily. It is 6" by 2-1/2". I also have mine in a case, so it measures a little bigger. Not sure how big a S9+ is, but if it is the same as mine or smaller there should be no problem.

Will a water bottle fit in one of the elasticised side pockets?

I don’t think so. My cell phone would not fit. It’s one reason I returned the purse. Those side pockets would fit something small like keys or chapstick. The elastic is tight but might loosen as the pocket is used.

What color is the lining inside each purse? It appears to be black in the photos.

The color of the lining is the same color as the outside of the purse. I would strongly suggest that you keep looking for something else. It won't last very long. The zippers on this purse are extremely cheap and will break to the point that they will not work after a few months of use. I had purchased this back in February of this year and I had to throw it out by September because I had 2 zippers that had broken. One on the inside and one of the main zippers on the outside.