I tested all LN mobile wallets (see my detailed guide here) but none of them have the option for adding a WT for your channels.

We are talking here about mobile LN nodes, NOT node management apps like Zeus, Zap, FullyNoded, Hexa etc, where the WT is configured on the node side not on the app.

Yes, with some of them like Phoenix, Breez, Nayuta, Bitkit, Electrum (trampoline) you have to trust their LSP offered in app, that will not cheat over your balance (you cannot open channels with specific nodes, only in Breez you can do it but not easy for noobs).

With OBW, Blixt, Electrum (non-trampoline), Valet the situation is different. Why? Because with these ones you can open channels with any node you want, including your own desktop node, from home. So you will trust yourself. In this way you could use a public routing node as your own LSP for your mobile LN node. As I explained in this other guide. Or this scenario using hosted channels, using fiatjaf's Poncho and OBW.

But still, if you want to open with other nodes, you do not have the option to add a WT. I know that Blixt is willing to add this feature, but not right now. Blixt is a full LND node.

Anyways, a WT on a mobile node I do not see it as urgent. Is not supposed to keep a large amount of money on your mobile, but just enough to do your regular shopping and having a lot of activity, not just a dormant useless channel.

Also some of public nodes, if you open private channels with them (on mobile node you open only private channels), will not keep too much time your channel open, due to not being efficient for them if you do not have activity.

General advice: open private channels ONLY with well known nodes, that you can stay in contact, have good liquidity and willing to offer you LSP for your mobile node. Example of such list here.