Yes, two waves can have the same frequency and wavelength but different amplitudes and still be in phase with each other. In wave terminology, "phase" refers to the relative position of two waves with respect to each other at a given point in time. Waves that are in phase have their crests and troughs aligned, while waves that are out of phase have their crests and troughs offset.
The amplitude of a wave determines its intensity or magnitude, while the frequency and wavelength determine its characteristics such as pitch and spatial extent. The amplitude of a wave is the maximum displacement or height of the wave from its equilibrium position. Two waves with different amplitudes can still have the same frequency and wavelength, meaning they oscillate at the same rate and have the same spatial length between consecutive crests or troughs.
For example, consider two sinusoidal waves with the same frequency and wavelength but different amplitudes. Wave A has a larger amplitude than Wave B. If the crests and troughs of both waves line up at the same points in space at a given moment, they are said to be in phase. The relative amplitudes of the waves do not affect their phase relationship, as long as their crests and troughs align.
It's important to note that the amplitude of a wave affects its energy content and intensity, but it does not directly influence its phase relationship with other waves.