You're mixing up some terminology here, so starting with vocabulary, a "wide angle lens" is one that can go wide and give a you a very large field of view--a lens that takes in the scene. What "25mm wide angle" means is that when you're zoomed all the way out, the field of view you have is equivalent to what a 25mm lens would see on a 35mm film camera.
Your Samsung WB1100F's lens is a superzoom. That means it has a zoom factor of over 10x (e.g., 35x), and the 35 is reached by simply dividing the longest focal length in its zoom range by the shortest one. Since you have a 4.5mm-157.5mm lens, that means 157.5/4.5 => 35x. And yes, that is a very very large zoom factor. Zoom factors are typically used by marketing, with most consumers assuming more is better, but in fact, the larger the zoom factor, often the more image quality compromises there may be in the lens to cover the very large zoom range, and the slower (smaller max. aperture) the lens may have the more it's zoomed in. Also, zoom factors are only a relative measure of how large the zoom range is, but isn't necessarily a good description of how the lens actually behaves/looks, since a 100-1000mm lens and a 5-50mm lens are both 10x zooms, but would have vastly different behavior.
This is why we like focal lengths. They're an absolute measure of the magnification of the lens.
The second thing to know here is that the sensor in your WB1100F is small. Smaller than a frame of 35mm film by a factor of about 5.5x. So while the film "equivalent" of your 4.5-157.5mm is 25-875mm on a film camera, it's still only a 4.5-157.5mm lens and a sensor 1/5th the size of a frame of film.
The advice about 70-135mm for portraits is mostly for folks using cameras with sensors that are the same size as a frame of 35mm film. The working distance/framing characteristics are going to be very different in that focal length range on that size of sensor than it will be on your camera. So simply using those focal lengths will not guarantee you the same behavior.
You aren't going to get the same result, because you'll be using a substantially different lens. I have a 5DMkII and a 135L. That 135 lens is great for portraits on full frame, because it opens up to a f/2. Your lens @157.5mm can only open to f/5.9. You'll have to stand farther back from your subject, too, than I would, to frame a subject identically, so you'd have an even deeper DoF, and you might run into pincushion distortion. If you switch to the field-of-view equivalent focal length for your sensor's format, 135/5.5 => 27mm, so you could stand at the same place to frame the same way, you'd still have less aperture than f/2, so you'd still have a deeper DoF, and you'd probably end up with barrel distortion from the shorter focal length.
The advice about short telephoto lenses presupposes a specific size of sensor, and a fast (f/2.8 or wider) lens. Your bridge camera has neither, so it doesn't behave the same way.
The problem with the superzoom on a bridge camera is that you're basically going to be trading off factors that will still keep you from getting a head-shot with a blurred background (which is what most people think of as portrait shots). It's mostly due to the sensor size. Background blur is controlled by four factors:
- Camera-to-subject distance (closer => more blur)
- Subject-to-background separation (farther apart => more blur)
- Aperture setting (the smaller the f-number/larger the aperture => more blur)
- Focal length (the longer the lens => more blur)
If you use a longer focal length, you have to increase the camera-to-subject distance and your max. aperture gets smaller.
The easiest way to get background blur with a 1/2.3" format sensor camera is to shoot macro. So, zooming out, moving in, and opening up the aperture is liable to get you the best background blur, but may cause barrel distortion which can be less than flattering to a subject.
