Try using more basic, buffered liquid:

"The phenol red modified Bst 2.0 reaction buffer (pH ~8.6–8.8) was prepared as fallow: 10 mM (NH4)2SO4, 8 mM MgSO4, 50 mM KCl, 0.1% v/v Tween 20, 0.8 M Betaine, 1.4 mM dNTP solution mix, phenol Red 0.1 mM"

A loop-mediated isothermal amplification (LAMP) assay for rapid detection of fumonisin producing Aspergillus species - ScienceDirect

Thank you for the answer Adam Figarski but i want to know how to make stock of phenol red?? is it ok to use NaOH as diluent? will it affect the LAMP reaction

How much of phenol red You need in Your preparation? Like in one batch of reagents You are preparing?

I would avoid introducing interfering ions to such sophsticated buffer. What is Your salt of choice of dNTP-s? Lithium? Sodium? What will You balance with pH of the final buffer?