On our April 2015 trip, we went glacier trekking, and the concern was more for snow protection than for falling rain, but our Gore-Tex jackets and bibs offered protection from both. You may be going at a rainier place and time of year, and might be wearing fewer insulating layers of long underwear.
If the Columbia pants are designed a little loose, to slip over other layers, they should work. I have at least one pair of navy blue Columbia rain pants, and pairs of other brands, but usually have put them on over hiking shorts and bare legs in warmer weather. Are your existing hiking pants made of cotton, or nylon, or some combination of fabrics? Your hiking pants may provide some rain resistance already.
We also have Showers Pass brand bicycling rain gear, which is designed for bike touring, but also worked while hiking in England.
A key feature is not only whether the rain gear is waterproof, but whether it’s also “breathable,” like Gore-Tex. A coated but not breathable fabric may shed water, but if you’re moving and sweating, and if that rain gear traps that moisture inside your pants or jacket, you can get wet and cold from your perspiration, even if no rain’s getting through. What specifications are described about the Columbia rainwear? Are there vented zippers, grommets, waist cinches? Those features can help the garments fit and perform better.
A Zip-lok bag can keep your smartphone dry, as long as it’s inside the bag. Our compact Olympus camera was specially designed to be extra shock and water resistant, and there are scuba diving cases for cameras that would probably be overkill, but there are other types of cases, made from vinyl or other materials that a camera or camping store might suggest. Our pack covers came with the backpacks, but you can get generic small, medium, large, or XL covers from REI or another outdoors supplier. Those don’t have to be breathable, just waterproof, and should have elastic around the opening and/or a draw cord to help ensure a snug fit on the pack, to keep out the elements.
Our whale watching tour provided waterproof coveralls onboard.