Are you starting with a .gpx file (e.g. from Audax org) and using that on the Xperia? What software do you use?
The applications I use can take gpx files from the audax web site or ones I create myself. I tend to use map my ride if I am pre-planning a route.
Software is generally ipbike in the foreground for cycling stats and route following BUT because ipbike is not a navigation application I now also run osmand in the background for voice navigation instructions.
I use the same phone a lot for google navigation in the car but in this case I'm just saying get me there so follow the route it proposes.
Pre-planned routes are a doddle and with map my ride the main issue is stopping the application from wandering off up bridle paths and anything else it thinks is a viable road. To do a preplanned off road (i.e. not following footpath, bridle ways or farm tracks ) is easy though, you just turn off road following and draw the lines on the map where you want to go by placing waypoints, then when you get back to a road, just tuen on road following again. I've easily navigated 300k Audax using gpx from the Audax web site and ones I've recreated on map my ride.
I now start with a battery pack plugged in because this means if I have to unplug due to rain I always have a phone with 100% charge which is good for 4-5 hours with the screen at full brightness. I could now very likely get much longer run time as my use of osmand means I'm willing to turn off the screen if there are issues and just follow the voice instructions.
I carry my battery packs in a top tube bag which is also convenient for stuffing a few gels or easily accessible sweets.
I have two external battery packs. One lets me do a 200k Audax with just the phone charged and itself. That has to be recharged at the mains. I have a second external battery pack that takes two 18650 lithium batteries. As I have a number of these batteries for torches this offers great flexibility, particularly as you can also charge batteries from the mains in the battery pack.
I use a sony xperia z ultra which has a 6.4 inch screen and I always get comment when anyone sees it. But at 57 I am very shortsighted and wear varifocals so the larger screen I find helpful. This phone can now be had for around £250. Ipbike has a facility to lock the screen which I normally do when riding so that drops of water on the screen are not interpreted as finger pressess. The phone is waterproof but not when charging, so making sure you have a full charge is helpful for when the rain does start. I have filled the phone with water on at least two occasions due to failing to close the usb port properly, but each time the phone has come back to life following a few days drying in the airing cupboard with all ports open.
The handlebar mount is quick relase which means it is easy to move from bike to bike (about £10 from ebay) but releasing the phone from the mount is even quicker. In the 9 months + that I've used the phone it has never come adrift whilst riding and that includes some scarily (almost 50 mph) descents and some offroad sportives.
When I had a Bryton I found that on sunny days it was necessary to have the screen backlight on at full brightness to get good visibility through cycling glasses. In this case I only got about 7 hours run time.