It will take a lot of tweaking and accessories to reach something like the pic you posted with the camera of a smartphone - no matter the brand.
It is not possible to take a picture with “no ISO” (such thing doesn’t exist), but what you are looking for here is the lowest possible ISO setting your MX5 can get. And as you explained, you would want to work with a relatively long exposure time - therefore some kind of a stand/tripod wouldn’t hurt. It depends on what kind of a water stream you are working with - if you have the exact circumstances as in the photo you attached a shutter speed of a half a second should already be enough.
Increasing the shutter speed, however, also increases the brightness of the picture. Especially during daylight your photos are heavily prone to turn out over-exposed - no matter what kind of a camera you use. To avoid this, professional photographers use ND filters (neutral density), which basically let less of the light inside the image sensor. This way they can take longer-exposure shots and turn the water flow silky smooth - and most of the filters even add a cool tint and feel to the picture. It’s not any kind of extreme science but even for a complete manual control DSLR camera it requires extra work, accessories and some experimenting - therefore, using a smartphone, don’t expect this to be easy as simply taking a photo with a filter or something like that.
I suggest you try a ND filter specifically made for a smartphone (or DIY) and play around with everything Google Play has to offer. The more manual control you can get over your smartphones camera, the better. Play around with the settings you are given by the best camera app you can find - but don’t forget the filter. It is the key here if you really want to achieve the extreme level of smartphone photography. You could do lots of other cool stuff with the filter as well.