discourse-placeholder-theme-component/mobile/mobile.scss

.d-wrap[data-wrap="placeholder"] {
  .discourse-placeholder-name {
    width: 50%;
    min-width: auto;
  }

  p {
    max-width: 40%;
  }

  .discourse-placeholder-value,
  .discourse-placeholder-select {
    width: 100%;
  }
}